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SubjectRe: [RFC][PATCH 3/4] Memory controller soft limit organize cgroups
On Thu, 08 Jan 2009 00:11:28 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> From: Balbir Singh <balbir@linux.vnet.ibm.com>
>
> This patch introduces a RB-Tree for storing memory cgroups that are over their
> soft limit. The overall goal is to
>
> 1. Add a memory cgroup to the RB-Tree when the soft limit is exceeded.
> We are careful about updates, updates take place only after a particular
> time interval has passed
> 2. We remove the node from the RB-Tree when the usage goes below the soft
> limit
>
> The next set of patches will exploit the RB-Tree to get the group that is
> over its soft limit by the largest amount and reclaim from it, when we
> face memory contention.
>

Hmm, Could you clarify following ?

- Usage of memory at insertsion and usage of memory at reclaim is different.
So, this *sorted* order by RB-tree isn't the best order in general.
Why don't you sort this at memory-reclaim dynamically ?
- Considering above, the look of RB tree can be

+30M (an amount over soft limit is 30M)
/ \
-15M +60M
?

At least, pleease remove the node at uncharge() when the usage goes down.

Thanks,
-Kame




> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
>
> mm/memcontrol.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 78 insertions(+)
>
> diff -puN mm/memcontrol.c~memcg-organize-over-soft-limit-groups mm/memcontrol.c
> --- a/mm/memcontrol.c~memcg-organize-over-soft-limit-groups
> +++ a/mm/memcontrol.c
> @@ -28,6 +28,7 @@
> #include <linux/bit_spinlock.h>
> #include <linux/rcupdate.h>
> #include <linux/mutex.h>
> +#include <linux/rbtree.h>
> #include <linux/slab.h>
> #include <linux/swap.h>
> #include <linux/spinlock.h>
> @@ -119,6 +120,13 @@ struct mem_cgroup_lru_info {
> };
>
> /*
> + * Cgroups above their limits are maintained in a RB-Tree, independent of
> + * their hierarchy representation
> + */
> +static struct rb_root mem_cgroup_soft_limit_exceeded_groups;
> +static DEFINE_MUTEX(memcg_soft_limit_tree_mutex);
> +
> +/*
> * The memory controller data structure. The memory controller controls both
> * page cache and RSS per cgroup. We would eventually like to provide
> * statistics based on the statistics developed by Rik Van Riel for clock-pro,
> @@ -166,12 +174,18 @@ struct mem_cgroup {
>
> unsigned int swappiness;
>
> + struct rb_node mem_cgroup_node;
> + unsigned long long usage_in_excess;
> + unsigned long last_tree_update;
> +
> /*
> * statistics. This must be placed at the end of memcg.
> */
> struct mem_cgroup_stat stat;
> };
>
> +#define MEM_CGROUP_TREE_UPDATE_INTERVAL (HZ)
> +
> enum charge_type {
> MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
> MEM_CGROUP_CHARGE_TYPE_MAPPED,
> @@ -203,6 +217,39 @@ pcg_default_flags[NR_CHARGE_TYPE] = {
> static void mem_cgroup_get(struct mem_cgroup *mem);
> static void mem_cgroup_put(struct mem_cgroup *mem);
>
> +static void mem_cgroup_insert_exceeded(struct mem_cgroup *mem)
> +{
> + struct rb_node **p = &mem_cgroup_soft_limit_exceeded_groups.rb_node;
> + struct rb_node *parent = NULL;
> + struct mem_cgroup *mem_node;
> +
> + mutex_lock(&memcg_soft_limit_tree_mutex);
> + while (*p) {
> + parent = *p;
> + mem_node = rb_entry(parent, struct mem_cgroup, mem_cgroup_node);
> + if (mem->usage_in_excess < mem_node->usage_in_excess)
> + p = &(*p)->rb_left;
> + /*
> + * We can't avoid mem cgroups that are over their soft
> + * limit by the same amount
> + */
> + else if (mem->usage_in_excess >= mem_node->usage_in_excess)
> + p = &(*p)->rb_right;
> + }
> + rb_link_node(&mem->mem_cgroup_node, parent, p);
> + rb_insert_color(&mem->mem_cgroup_node,
> + &mem_cgroup_soft_limit_exceeded_groups);
> + mem->last_tree_update = jiffies;
> + mutex_unlock(&memcg_soft_limit_tree_mutex);
> +}
> +
> +static void mem_cgroup_remove_exceeded(struct mem_cgroup *mem)
> +{
> + mutex_lock(&memcg_soft_limit_tree_mutex);
> + rb_erase(&mem->mem_cgroup_node, &mem_cgroup_soft_limit_exceeded_groups);
> + mutex_unlock(&memcg_soft_limit_tree_mutex);
> +}
> +
> static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
> struct page_cgroup *pc,
> bool charge)
> @@ -917,6 +964,10 @@ static void __mem_cgroup_commit_charge(s
> struct page_cgroup *pc,
> enum charge_type ctype)
> {
> + unsigned long long prev_usage_in_excess, new_usage_in_excess;
> + bool updated_tree = false;
> + unsigned long next_update;
> +
> /* try_charge() can return NULL to *memcg, taking care of it. */
> if (!mem)
> return;
> @@ -937,6 +988,30 @@ static void __mem_cgroup_commit_charge(s
> mem_cgroup_charge_statistics(mem, pc, true);
>
> unlock_page_cgroup(pc);
> +
> + mem_cgroup_get(mem);
> + prev_usage_in_excess = mem->usage_in_excess;
> + new_usage_in_excess = res_counter_soft_limit_excess(&mem->res);
> +
> + next_update = mem->last_tree_update + MEM_CGROUP_TREE_UPDATE_INTERVAL;
> + if (new_usage_in_excess && time_after(jiffies, next_update)) {
> + if (prev_usage_in_excess)
> + mem_cgroup_remove_exceeded(mem);
> + mem_cgroup_insert_exceeded(mem);
> + updated_tree = true;
> + } else if (prev_usage_in_excess && !new_usage_in_excess) {
> + mem_cgroup_remove_exceeded(mem);
> + updated_tree = true;
> + }
> +
> + if (updated_tree) {
> + mutex_lock(&memcg_soft_limit_tree_mutex);
> + mem->last_tree_update = jiffies;
> + mem->usage_in_excess = new_usage_in_excess;
> + mutex_unlock(&memcg_soft_limit_tree_mutex);
> + }
> + mem_cgroup_put(mem);
> +
> }
>
> /**
> @@ -2218,6 +2293,7 @@ mem_cgroup_create(struct cgroup_subsys *
> if (cont->parent == NULL) {
> enable_swap_cgroup();
> parent = NULL;
> + mem_cgroup_soft_limit_exceeded_groups = RB_ROOT;
> } else {
> parent = mem_cgroup_from_cont(cont->parent);
> mem->use_hierarchy = parent->use_hierarchy;
> @@ -2231,6 +2307,8 @@ mem_cgroup_create(struct cgroup_subsys *
> res_counter_init(&mem->memsw, NULL);
> }
> mem->last_scanned_child = NULL;
> + mem->usage_in_excess = 0;
> + mem->last_tree_update = 0; /* Yes, time begins at 0 here */
> spin_lock_init(&mem->reclaim_param_lock);
>
> if (parent)
> _
>
> --
> Balbir
> --
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